Xue-Wang Gao

A Cascade Cross-Coupling Hydrogen Evolution Reaction by Visible Light Catalysis

Cross-dehydrogenative-coupling reaction has long been recognized as a powerful tool to form a C-C bond directly from two different C-H bonds. Most current processes are performed by making use of stoichiometric amounts of oxidizing agents. We describe here a new type of reaction, namely cross-coupling hydrogen evolution (CCHE), with no use of any sacrificial oxidants, and only hydrogen (H2) is generated as a side product. By combining eosin Y and a graphene-supported RuO2 nanocomposite (G-RuO2) as a photosensitizer and a catalyst, the desired cross-coupling products and H2 are achieved in quantitative yields under visible light irradiation at room temperature.

Cross-coupling hydrogen evolution reaction in homogeneous solution without noble metals.

A highly efficient noble-metal-free homogeneous system for a cross-coupling hydrogen evolution (CCHE) reaction is developed. With cheap, earth-abundant eosin Y and molecular catalyst Co(dmgH)2Cl2, good to excellent yields for coupling reactions with a variety of isoquinolines and indole substrates and H2 have been achieved without any sacrificial oxidants. Mechanistic insights provide rich information on the effective, clean, and economic CCHE reaction.

Cobalt-Catalyzed Cross-Dehydrogenative Coupling Reaction in Water by Visible Light

By using catalytic amount of CoCl2 with dmgH (dimethylglyoxime) as ligand to form a photosensitizer in situ, a highly selective, efficient, and environmentally benign visible light mediated cross-dehydrogenative coupling (CDC) reaction has been developed in aqueous medium. The desired cross-coupling C-C bonds that involve Csp3 with Csp, Csp2, and Csp3, respectively, were achieved exclusively in high yields without formation of any other byproduct.

A unique 1,2-acyl migration for the construction of quaternary carbon by visible light irradiation of platinum(II) polypyridyl complex and molecular oxygen.

A unique 1,2-acyl migration for the construction of quaternary carbon in a one-pot reaction under visible light is described. By irradiating a platinum(II) polypyridyl complex with visible light, enamine 1 is able to react with alcohol 2 to yield compound 3 featuring a quaternary carbon via 1,2-acyl migration and concurrent esterification. Studies on the mechanism reveal that the platinum(II) complex is able to generate singlet oxygen ((1)O2) that is responsible for this unprecedented intramolecular 1,2-acyl migration transformation.

Microstructure and photoluminescence properties of bulk-quantity SnO2 nanowires coated with ZnO nanocrystals

Large-quantity single-crystal SnO2 nanowires coated with ZnO nanocrystals (nc-ZnO/SnO2 nanowires) were directly synthesized by a one-step thermal evaporation process. SnO2 nanowires were single-crystalline tetragonal structures with the diameters and lengths of 50–100 nm and several tens of micrometres, respectively. ZnO nanocrystals were single-crystalline wurtzite structures with average diameters less than 5 nm, which coated the whole SnO2 nanowires uniformly. Photoluminescence measurements showed that the nc-ZnO/SnO2 nanowires had a much stronger near-band UV emission (at 393 nm) than pure SnO2 nanowires. The Sn doping into ZnO nanocrystals may be a most possible reason for the redshift and broadening of UV emission peaks from nc-ZnO/SnO2 nanowires. The microstructure and photoluminescence properties of the nc-ZnO/SnO2 nanowires are discussed.

A Redox Shuttle Accelerates O2 Evolution of Photocatalysts Formed In Situ under Visible Light

A redox shuttle strategy is demonstrated to be a promising approach to accelerate hole removal for efficient O2 production with mesoporous graphitic carbon nitride, WO3 , BiVO4 , NiTi-LDH, and Ag3 PO4 water-oxidation catalysts under visible-light irradiation.

Reactivity and mechanistic insight into the cross coupling reaction between isochromans and β-keto esters through C–H bond activation under visible light irradiation

The visible light catalytic cross coupling reaction from two different C–H bonds provides an efficient protocol for C–H bond activation and C–C bond construction. The application of the oxidative photoredox strategy to couple C–H bonds next to an oxygen atom with other C–H bonds is more challenging because of the more positive oxidation potential of ethers than that of amines. Here, we take advantage of organic dye 9-mesityl-10-methylacridinium perchlorate (Acr+-Mes ClO4−) as the photosensitizer and BrCCl3 as the terminal oxidant to achieve the addition of β-keto esters to oxonium species, directly generated from isochromans, leading to the formation of alkylation products in the α-position of an oxygen atom under visible light irradiation.

Homocoupling of 3-Halooxindole via Visible-Light Photocatalysis: A Mild Access to 3,3′-Bioxindoles

This paper introduces a simple way to the homocoupling of tertiary halides induced by photocatalysis. This method features mild reaction conditions, excellent functional group tolerance, high yields, low photocatalyst loading and successful application to the highly sterically hindered systems. On the basis of the reaction results, a novel stable-radical-induced homocoupling reaction mechanism has been proposed.

Identifying key intermediates generated in situ from Cu(II) salt–catalyzed C–H functionalization of aromatic amines under illumination

Cu(II) salts can activate C–H bonds of aromatic amines or imines to construct C–C bonds in air without external photosensitizer. Copper compounds involved in photocatalysis have recently spurred considerable interest for their novel transformations. However, mechanistic investigations are still in infancy. We find a new type of reaction, that is, Cu(II) salt–catalyzed C–H functionalization of aromatic amines triggered by visible light irradiation. An array of mechanistic observations, including high-resolution mass spectrometry, ultraviolet-visible absorption spectrum, electron spin resonance, x-ray absorption near-edge structure, and density functional theory calculation, have identified the key intermediates generated in situ in the transformation. Integration of single-electron transfer, singlet oxygen (1O2), and new absorption species, intermediate I and intermediate II formed in situ from Cu(II) salts and substrate amines or imines, respectively, is responsible for the N–H and C–H bond activation of secondary amines to couple with nucleophiles in air, thereby leading to the formation of quinoline, indolo[3,2-c]quinoline, β-amino acid, and 1,4-dihydropyridine derivatives in moderate to good yields under visible light irradiation at room temperature.

Self-assembled vesicles from amphiphilic platinum(II) terpyridyl complex in water

A new cationic amphiphile (1) functionalised with platinum(II) terpyridyl unit was designed and synthesised to realize self-assembly in water. Using UV–vis and emission spectroscopy, scanning electron microscopy, cryogenic transmission electron microscopy, dynamic light scattering and time-correlated single-photon counting technique, we have demonstrated that amphiphile 1 can self-assemble into stable vesicular aggregates upon direct dissolution in water, which is rarely observed in the literature.